Generally, as is well known in the art or technique of shelf or off-shore drilling for gas and/or oil, riser lines are employed with such riser lines being usually comprised of a plurality of sections or lengths of generally rigid pipe interconnected in end-to-end relationship. Also as is generally well known, such riser lines are often subjected to great stresses and loads occassioned as by bending moments or force couples applied thereto. Such forces, moments and/or couples may be generated by, for example, the riser line being supported as by a ship, floating platform or other vessel and having such floating support, in turn, undergo changes in position or attitude because of wave movements or the like.
Accordingly, the prior art has, heretofore, attempted to provide articulated connections instead of rigid joints as between succeeding pipe sections forming the riser line in order to achieve a reduction in the bending moments otherwise experienced by such a riser line. Specifically, the prior art has suggested the use of ball and socket type joints or rubber (or rubber-like) rings for such articulated connections. Such prior art devices have not been found to be satisfactory. For example, among other problems, ball and socket joints exhibit a significant degree of friction which, in turn, causes abrupt stresses to occur often resulting in damage to the related pipe and overall riser line. Even though the use of prior art intermediate members consisting of rubber (or similar material) rings has the advantage of exhibiting only a comparatively slight degree of friction, such prior art rubber ring members are not capable of carrying loads of a magnitude sufficiently great to make such prior art rubber rings totally satisfactory.
Further, the prior art has heretofore suggested, as generally disclosed in U.S. Pat. No. 3,523,578, the use of cardan joints as the single connection between succeeding pipes instead of a rigid pipe connection or joint. Theoretically, such a cardan pipe joint should achieve a considerable reduction in the bending moment otherwise experienced by the riser line because a cardan joint, if maintained is substantially perfect condition, will not transmit any moments therethrough. However, use of such prior art cardan joints has shown that they have serious disadvantages. For example, a pipe joint, used in an environment such as a riser line, is subjected to very high stresses and accordingly the cardan joint structure must be made physically large enough to withstand such anticipated stresses. However, this, in turn, results in an extremely large diameter of the cardan casing often of a magnitude even possibly precluding its use in a riser line system. Furthermore, there is always the danger (often actually experienced) that the cardan casing will become somewhat (even slightly) deformed thereby making the joint susceptible to total failure. Also, effective and reliable fluid sealing to a cardan joint is, to say the least, difficult.
Accordingly, the invention as herein disclosed and claimed is primarily directed to the solution of the foregoing and other attendant or related problems.